A lot of rifles have been rebuilt, Particularly Vietnam era rifles. Ordinarily the barrels ended up replaced. Some examples of markings found on replacment barrels contain: Yes, I am sure the upper receiver is Colt, combined with the BCG. It is basically the barrel that's questionable to me. Some 1969 https://coltcombatelitecommander402333.eqnextwiki.com/4552129/the_fact_about_colt_combat_unit_rail_gun_45_that_no_one_is_suggesting